The present invention relates to a method for easily measuring a brake mean effective pressure of a vehicle such as an automobile actually running on a road.
Generally, a brake mean effective pressure is used as an index indicative of engine performance of an automobile. Although the brake mean effective pressure has a unit of pressure, it can be considered as a torque per engine displacement.
For example, a motive force F represented by the following equation (1):
F=A+BV2+mxcex1+mgxcex8xe2x80x83xe2x80x83(1)
wherein
A: rolling resistance
BV2: (aerodynamic drag)
B=CDxc3x97Sxc3x97xcex3a/g
CD: drag coefficient, S: maximum vehicle cross-section, xcex3a: specific weight of air, g: gravitational acceleration of gravity, V: vehicle speed
m: vehicle weight, a: acceleration of vehicle, xcex8: gradient angle
Of the above values, A and B can be determined by a coast down method, and V and  can be determined by a vehicle speed sensor. In the case of the coast down method, a gearshift lever is placed into neutral at a certain speed on a flat road and the vehicle is allowed to coast (coasting running) while the values of A and B are obtained from the deceleration. That is, in the above equation (1), F=O, xcex8=0, and xe2x88x92m=A+BV2.
However, in the case of a vehicle running on a road, it is difficult to obtain the gradient of the road precisely and, thus it is difficult to obtain the Road Load (RL) and motive power in all road conditions. It is conventional method to mount a torque sensor to an axle shaft or a driving wheel to obtain the RL of an automobile. However, the torque sensor may project from a car body, and its durability may not be sufficient. Furthermore, the torque sensor is not suitable for running on an ordinary road. Therefore, such a sensor is used mainly for measuring procedures on a test course, and the sensor can not be used for measurement on an ordinary road.
The present invention has been accomplished in view of the above circumstances, and it is an object of the invention to provide a method for easily measuring a brake mean effective pressure of a running vehicle.
To achieve the above object, an air flow sensor, a xcex sensor and a data collecting apparatus are mounted to a vehicle. The running speed (Km/R) and engine speed (rpm) of the vehicle while actually running on a road surface, and output of the air flow sensor and the xcex sensor are inputted into the data collecting apparatus. A specific fuel consumption is obtained from an intake air amount and ratio of excessive air in exhaust gas. The output of an engine is obtained from a relation between the specific fuel consumption and engine speed.